Boris Johnson has issued a blistering attack on Theresa May's Brexit strategy just days before the Conservative Party conference.
The former foreign secretary, who sensationally quit the Cabinet in July, described the Prime Minister's Chequers plan as "a moral and intellectual humiliation for this country" that will "cheat the electorate" if implemented.
Mr Johnson, in a Telegraph op-ed, accused the Government and civil service of a "pretty invertebrate performance" in negotiations and said there had been "a collapse of will by the British establishment to deliver on the mandate of the people".
In a 4,500-word column, entitled "A better plan for Brexit", Mr Johnson also set out an alternative vision which he says would make Britain "rich, strong and free".
As a priority, the former London mayor urged the Government to ditch Chequers and negotiate a Canada-style free deal which would "fulfil the instruction of the people".
He said: "Overall, the Chequers proposals represent the intellectual error of believing that we can be half-in, half-out: that it is somehow safer and easier for large parts of our national life to remain governed by the EU even though we are no longer in the EU.
"They are in that sense a democratic disaster. There is nothing safe or 'pragmatic' in being bound by rules over which we have no say, interpreted by a federalist court.
"The Chequers proposals are the worst of both worlds. They are a moral and intellectual humiliation for this country. It is almost incredible that after two years this should be the opening bid of the British government."
Mr Johnson also argues for a new withdrawal agreement which states that the Irish border question will be settled as part of the deal on the future economic arrangements.
He further argues that the implementation period should be used to negotiate and bring into force a "SuperCanada" type free trade agreement and says MPs should not vote to hand over £40 billion to the EU without any such agreement.
He adds: "This is the time to get it right. This is the approach that allows this country really to exploit the opportunities of Brexit, to diverge and legislate effectively for the new technologies and businesses in which the UK has such a lead.
"This is an opportunity for the UK to become more dynamic and more successful, and we should not be shy of saying that - and we should recognise that it is exactly this potential our EU partners seek to constrain."
Mr Johnson concludes by issuing a rallying cry to the Tory base, saying "this is the moment to change the course of the negotiations and do justice to the ambitions and potential of Brexit", and warning "that future generations will not lightly forgive us if we fail".
The intervention comes two days before the start of the Conservative Party conference in Birmingham where Brexit is expected to feature heavily.
Mr Johnson's comments also come after the current Foreign Secretary Jeremy Hunt called for calm over the current Brexit impasse - claiming there was always going to come a point in negotiations "where everyone was looking into the abyss".
Mr Hunt also backed the Prime Minister's resolve and warned the EU and doubters in the UK that "underestimating Theresa May is one of the biggest mistakes that you could make right now".
Mrs May's Chequers plan was publicly rejected by EU leaders in Salzburg last week and both Labour and Tory Eurosceptics said they would vote against any such proposal.